1,720,970 research outputs found
Innovative green technologies for the recovery of strategic metals from residues
Full text linkL’obiettivo di questa tesi è quello di sviluppare delle procedure sostenibili per il recupero di metalli preziosi da circuiti stampati a fine vita (PCB), nell’ottica del riciclo dei rifiuti elettronici. Una delle tecniche più innovative per l’estrazione dei metalli preziosi da PCB è il processo di bioleaching, che impiega i microorganismi. A questo proposito la capacità del batterio Pseudomonas aeruginosa di produrre cianuro e mobilizzare Ag e Au da PCB è stata analizzata. I risultati hanno mostrato una mobilizzazione del 90% di Ag e 20% di Au. Considerando l'attuale disponibilità di PCB sul mercato, questi risultati sono molto promettenti per lo sviluppo dei processi di riciclo. Una strategia per aumentare l’estrazione di Au può essere la rimozione di Cu, che è uno dei maggiori competitori, o di Ag, così che il cianuro sintetizzato possa complessare più selettivamente l’Au. L'estrazione dei metalli preziosi è stata anche valutata con la tecnica della lisciviazione con tiosolfato, un’alternativa sostenibile all’utilizzo del cianuro. I risultati hanno dimostrato che la lisciviazione dei metalli preziosi è correlata alla diversa granulometria dei PCB. Inoltre, è stato effettuato uno studio preliminare per il recupero dei metalli dalla soluzione di tiosolfato. L’adsorbimento su resina ha permesso di separare il recupero del Cu da quello dei metalli preziosi, aumentando la purezza dei prodotti. Allo stesso modo, l'elettrodeposizione ha consentito il recupero del 90% dei metalli preziosi nelle prime 24 ore, con solo una piccola percentuale di Cu. I risultati di questo lavoro suggeriscono di combinare le due tecniche per un recupero selettivo dei metalli preziosi. Infine, è stata valutata la carbon footprint dei processi con l’analisi del ciclo di vita (LCA). La lisciviazione con il tiosolfato è risultata la scelta migliore per il recupero dei metalli preziosi in termini di maggior credito ambientale derivato dalle ottime rese di estrazione.Considering the continuous increase in the production of electronic waste, the aim of this thesis is to develop sustainable procedures for the recovery of precious metals from the end-of-life printed circuit boards (PCBs). One of the most innovative techniques for the extraction of precious metals is the bioleaching process, which employ microorganisms. In this regard, the ability of the cyanogenic bacteria Pseudomonas aeruginosa to produce cyanide and mobilize Ag and Au from PCBs was analysed. The results showed the mobilization of 90% Ag and 20% Au. Considering the current availability of PCBs on the market, these results are very promising for the development of recycling processes. A possible strategy for increase the extraction of Au can be the previous removal of Cu, that is one of the most interfering metals, or of Ag, thus the synthetized cyanide can complex more selectively with Au. The extraction of Au, Ag and Pd was also evaluated with a chemical leaching with thiosulfate, employed as an alternative to cyanidation. The results showed good extraction efficiencies based on the different granulometry of the PCBs. In addition, a preliminary study on the precious metal recovery from a thiosulfate solution with the resin adsorption and the electrodeposition technique was performed. The adsorption step on the anionic resin allowed to separate the recovery of Cu from that of precious metals, increasing the purity of the final products. Similarly, the electrodeposition allowed the recovery of 90% of the precious metals in the first 24 hours, with only a small percentage of Cu. The results suggest combining the two techniques for a selective recovery. Furthermore, the carbon footprint of bioleaching and thiosulfate leaching was evaluated with the life cycle assessment (LCA). The thiosulfate leaching represents the best choice for precious metals recovery in terms of greater environmental credit derived from the good extraction efficiencies
Environmental sustainability assessment of different strategies for the treatment of wastewater from textile industry
Full text linkSevere water consumption and highly polluted wastewater are the main issues of textile industries, which can affect environmental safety. Advanced oxidation processes (AOP) emerged as innovative strategies to enhance conventional wastewater treatments, for their strong ability to reduce chemical oxygen demand (COD) and pollutants. Among these, hydrodynamic cavitation (HC) stands out as a promising technique to minimize the chemical additive uses, thereby improving the process sustainability. A life cycle assessment (LCA) was conducted to compare four scenarios, traditional biological treatment, membrane treatment combined with AOP and HC used either as pre- or post-treatment to the biological process. The results showed that biological process followed by HC offers the lowest environmental impact. This is attributed to a configuration change (compared to HC as pre-treatment) that reduces energy consumption without compromising water quality. In the climate change category, one of the most relevant, HC as a post-treatment (scenario 4) reduces the impact by 94%, compared to HC pre-treatment (scenario 3). It also achieves around 30% impact reduction relative to biological treatment, while ensuring the highest water quality, with a 98% reduction in COD. This quality supports the potential for water recirculation within textile manufacturing. Furthermore, the possibility of water reuse offsets the environmental cost of producing high-quality water, with an average environmental credit between 440 (scenario 3) and 600 (scenario 1) m3-world eq, in the water use category. The superiority of the HC post-treatment setup was also confirmed from a performance standpoint, as it reduces the complexity of process management
The Green Indium Patented Technology SCRIPT, for Indium Recovery from Liquid Crystal Displays: Bench Scale Validation Driven by Sustainability Assessment
Full text linkIndium is considered a valuable and irreplaceable material for a variety of applications that improve the quality of human life. Due to its limited availability and the growing demand, it is mandatory to find sustainable solutions for indium recovery from end-of-life devices. The green indium patented technology SCRIPT (ITA202018000008207) focuses on recovering indium from ground LCD panels, developed through laboratory scale investigation. The process ensures high recovery efficiencies of indium (>90%), features a simple design, and fully exploits the solid residue with the production of a concrete for building applications. This manuscript presents a study focused on the validation and optimization of the patented SCRIPT technology at the bench scale, driven by sustainability assessment. Bench scale experiments successfully validated the technology, improving its technology readiness level. Furthermore, an environmental sustainability assessment highlighted the importance of treating the finest fraction, which has the highest indium concentration. Optimization tests at the bench scale demonstrated that water could be recirculated for more than five cycles. The economic sustainability tests highlighted that when the indium concentration in the material fed into the recycling plant is above 1000 mg/kg, the technology is cost effective and worth investment. Our study is fundamental for boosting indium recycling in the world. Moreover, our methodological approach represents a guideline for achieving sustainability goals within circular economy approaches for strategic metals in complex matrices
Optimization of Sustainable Processes for the Extraction of Precious Metals from End-of-life Printed Circuit Boards
No full textThe technology advancement and innovation has been very significant and fast, in the last decades. This aspect is particularly evident in the electric and electronic equipment (EEE) field, where new devices are produced every year. The manufacture development is translated in two main issues: the highest metal required and the greatest waste flows to manage. To solve this double criticality, the old linear management method, in which every product became a waste, must evolve in a circular approach based on the principle “resource-product-regenerated resource” (urban mining). The end-of-life printed circuit boards (PCB) represent one of the most significant wastes from electric and electronic equipment (WEEE). In addition to their availability, the interest for these scraps is mainly justified by the high precious metal concentration (e.g. gold, silver, and palladium), which makes them a promising secondary resource. Several approaches are developed for precious metal recoveries from PCB, mainly by pyrometallurgy or hydrometallurgy. Biohydrometallurgical and green hydrometallurgical processes, using more sustainable reagents, are gaining increasing prominence, for their possibility to decrease the environmental costs, compared to the most traditional hydrometallurgy with chemical cyanide lixiviant. The present work aims to supply two innovative solutions: biotechnology by Pseudomonas aeruginosa for the biological cyanide production, and a green-hydrometallurgical process, using the thiosulphate as lixiviant agent for precious metal (i.e. Au and Ag) recovery. The central composite design of a response surface methodology (CCD-RSM) is used to optimize the cyanide production by P. aeruginosa evaluating the influence of both initial pH and glycine concentration. The same statistical approach (CCD-RSM) is used to find the best operative conditions for the precious metal leaching from PCB by thiosulphate, assessing the interaction among sodium thiosulphate, total ammonia/ammonium, particle size and time. The experimental results are further enhanced by the carbon footprint assessment which has quantified the possible environmental advantages of the developed solutions of PCB recycling, able to integrate the circular economy principles
Non-toxic, high selectivity process for the extraction of precious metals from waste printed circuit boards
Full text linkThe work presented here focused on the extraction of gold (Au), silver (Ag) and palladium (Pd) from electronic waste using a solution of ammonium thiosulfate. Thiosulfate was used as a valid alternative to cyanide for precious metal extractions, due to its non-toxicity and high selectivity. The interactions between sodium thiosulfate, total ammonia/ammonium, precious metal concentrations and the particle size of the waste printed circuit boards (WPCBs) were studied by the response surface methodology (RSM) and the principal component analysis (PCA) to maximize precious metal mobilization. Au extraction reached a high efficiency with a granulometry of less than 0.25 mm, but the consumption of reagents was high. On the other hand, Ag extraction depended neither on thiosulfate/ammonia concentration nor granulometry of WPCBs and it showed efficiency of 90% also with the biggest particle size (0.50 < Ø < 1.00 mm). Pd extraction, similarly to Au, showed the best efficiency with the smallest and the medium WPCB sizes, but required less reagents compared to Au. The results showed that precious metal leaching is a complex process (mainly for Au, which requires more severe conditions in order to achieve high extraction efficiencies) correlated with reagent concentrations, precious metal concentrations and WPCB particle sizes. These results have great potentiality, suggesting the possibility of a more selective recovery of precious metals based on the different granulometry of the WPCBs. Furthermore, the high extraction efficiencies obtained for all the metals bode well in the perspective of large-scale applications. [Figure not available: see fulltext.
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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